Let me start by saying I love rust, but the supply chain story for official rust compiler binaries is not okay and I would never even trust them even on a dev workstation, let alone in production.

Most people get rust from rustup, an unsigned "curl | sh" style magic script.

Whoever controls the dns for rustup.rs, or the webserver, or the BGP nodes between you and the webserver, can just change that at any time, or change it only when requests come from specific IP addresses and backdoor people all day long.

Next you end up getting binaries of rust, that are not reproducible, and have no remote attestation provenance for the build system. Without at least one of those that means there is a CI, or workstation somewhere one or more people control building those binaries that could also tamper with them silently at build time. No one can reproduce them so until someone has the time to do some deep dive binary diffing, unlikely to be detected any time soon.

And then, we get to the fact the official rust releases are not full source bootstrapped. To build rust 1.94 you need rust 1.93 and so on. That means if you have ever backdoored -any- release of rust in the past using the above weaknesses, you have backdoored all of them via trusting trust attacks where the backdoor always detects when the next version of the rust compiler is being built and copies itself over to the new build.

The way you prove this is not happening within the rust build chain, is you bootstrap from another compiler. The rust team does not do this but thankfully Mutabah made mrustc, which is a minimal c++ port of the rust compiler suitable for building the actual rust compiler, so we can anchor our supply chain to a C compiler instead.

But now how do you trust the C compiler? Some random compiler from debian is at least signed, but only signed by one person. Another major risk.

So now you need to build your c compiler from source code all the way up, a technique called full source bootstrapping. A tiny bit of human reviewable machine code is used to build a more complex version of itself, all the way up to tinycc, gcc, llvm, and eventually rust. And then you have it all be deterministic and then have many people build any portions of the build chain that have changed every release and all get the same result, and sign that result. THEN we know you are getting a faithful build of the rust compiler from source that no one had the opportunity to tamper with.

That is how we build and release rust in stagex: https://stagex.tools/packages/core/rust/

Credit where due that Guix did this first, though they still have a much more relaxed supply chain security policy so threat model accordingly.

But how do you know the actual source of the stagex build process was not tampered by an impersonated maintainer that merged their own malicious PR made by a pseudonym bypassing code review? Well we sign every commit, and we sign every PR. Every change must have at least two cryptographic signatures by well known WoT established private keys held on smartcards by maintainers. We simply do not allow merging PRs from randos until another maintainer has signed the PR and then a -different- maintainer can review and do a signed merge. This also means no one can re-write git history, so we can survive a compromise even of the git server itself.

This is something only stagex does as far as we can tell, as our threat model assumes at least one maintainer is compromised at all times.

But, aside from a few large high risk entities, most people are not using stagex or guix built rust and just yolo using a shell script to grab a random binary and start compiling code with it.

I would strongly urge people to stop doing that if you are working on software meant to run on anything more security sensitive than a game console.

With the giant wave of AI bots doing account takeovers and impersonation all the time, github login as the last line of defense is going to keep ending badly.

Use provably correct binaries no single person can tamper with, or build them yourself.

Supply chain nightmare: How Rust will be attacked and what we can do to mitigate